Sarcopenia, defined here as reduced muscle mass, is common in older adults. It is a potentially modifiable contributor to muscle weakness, which is strongly related to decreased physical performance and disability. Sarcopenia remains difficult to diagnose, in part because proposed criteria have not been based on clinical outcomes, compared across data sets and/or formally evaluated for diagnostic test characteristics. For a novel condition or treatment, extensive structured evidence is needed to support formal consensus processes. Until then, the diagnosis of sarcopenia remains in limbo. While the diagnosis of sarcopenia is unclear, potential interventions are emerging rapidly, but many trials cannot be implemented until eligibility can be clearly defined. Thus progress toward clear diagnostic criteria for sarcopenia might aid in appraisal of existing literature, guide eligibility and measurement in future studies and help create indications for clinical treatments in practice. In order to address the need for further evidence about muscle mass, strength and aging, an initiative was developed under the aegis of the Foundation of the NIH (FNIH). Investigators representing nine studies and over 23,000 diverse older adults were selected to join the Sarcopenia Project Team, which has performed pooled analyses in support of criteria for clinically important weakness and low muscle mass, based on concurrent and predictive accuracy related to mobility disability. As a next step in building the evidence-base toward consensus on the diagnosis of sarcopenia, we propose to present our work for feedback and suggestions from scholars and health care professionals in relevant specialties. Based on a 2/12 day conference, we will present our conceptual framework, methods and findings, as well as potential relationships to other diagnostic approaches. We will use both structured surveys and interactive group approaches to assess agreement with our preliminary recommendations, guide further analyses, generate publications and seek written commentary by health professional organizations. Therefore the aims of this U13 proposal, a shared initiative of NIA, FNIH and multiple investigators, are to: 1) Present and discuss with a wide range of interested parties, the processes and results of the data analyses performed by the Sarcopenia Project Team, 2) Obtain recommendations for areas of agreement, remaining gaps in knowledge and further research, 3) Provide a venue for young investigators to engage in research on aging, sarcopenia, and diagnostic test development, and 4) Disseminate the results of our work. Our short term goals are to progress toward consensus on evidence-based criteria for the diagnosis of sarcopenia and to model a collaborative process for evidence-based diagnoses of other important geriatric health problems. Our long term goal is to achieve clinical recognition of sarcopenia and ultimately to define a pathway toward evidence-based clinical diagnostic guidelines for other complex problems of aging.